解决https调用出现【基础连接已经关闭: 未能为 SSL/TLS 安全通道建立信任关系】错误

在HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(url);前面添加

ServicePointManager.ServerCertificateValidationCallback = new System.Net.Security.RemoteCertificateValidationCallback(CheckValidationResult);

CheckValidationResult方法

 public static bool CheckValidationResult(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors errors)
{  // 总是接受  
　　return true;
}